This invention pertains to methods and systems for operating a cardiac rhythm management device in which both atria or both ventricles are sensed. In particular, the invention relates to a method and system for eliminating cross-talk due to far-field signals from a sensing channel.
Cardiac rhythm management devices are implantable devices that provide electrical stimulation to selected chambers of the heart (i.e., the atrium and/or ventricle) in order to treat disorders of cardiac rhythm. A pacemaker, for example, is a cardiac rhythm management device that paces the heart with timed pacing pulses. (As the term is used herein, a pacemaker is any cardiac rhythm management device with a pacing functionality regardless of any other functions it may perform such as cardioversion or defibrillation.)
The most common condition for which pacemakers are used is in the treatment of bradycardia, where the ventricular rate is too slow. Atrio-ventricular conduction defects (i.e., AV block) that are fixed or intermittent and sick sinus syndrome represent the most common causes of bradycardia for which permanent pacing may be indicated. If functioning properly, the pacemaker makes up for the heart""s inability to pace itself at an appropriate rhythm in order to meet metabolic demand by enforcing a minimum heart rate. Pacing therapy can also be used in the treatment of congestive heart failure (CHF), which is a clinical syndrome in which an abnormality of cardiac function causes cardiac output to fall below a level adequate to meet the metabolic demand of peripheral tissues. CHF can be due to a variety of etiologies with that due to ischemic heart disease being the most common. Some CHF patients suffer from some degree of AV block or are chronotropically deficient such that their cardiac output can be improved with conventional bradycardia pacing. It has also been shown, however, that some CHF patients suffer from conduction defects (e.g., bundle branch blocks) such that their cardiac outputs can be increased by improving the synchronization of cardiac contractions with electrical stimulation. In order to treat these problems, cardiac rhythm management devices have been developed which provide pacing stimulation to one or more heart chambers in an attempt to improve the coordination of atrial and/or ventricular contractions, termed cardiac resynchronization therapy.
Cardiac rhythm management devices that deliver resynchronization pacing to a heart chamber and its contralateral counterpart utilize sensing channels for each chamber in order to control the delivery of paces and for diagnostic purposes. It is possible, however, to misinterpret a depolarization occurring in one chamber as a sense in the opposite chamber. When a depolarization occurring in one chamber produces a far-field signal which is sensed in the sensing channel of the opposite chamber, a form of cross-talk between the sensing channels results.
The present invention is a system and method for eliminating cross-talk due to far-field signals from a sensing channel in a cardiac rhythm management device in which sensing channels are provided for a first heart chamber and a second heart chamber contralateral to the first chamber. In accordance with the invention, a sensing channel is rendered refractory for a specified time interval in order to avoid sensing both a chamber depolarization and a far-field signal from the opposite chamber during the same cardiac cycle.
The invention may be incorporated into an exemplary device for delivering ventricular resynchronization therapy in which paces are delivered to one or both ventricles based upon ventricular senses from one ventricle. In one embodiment, the ventricles are paced based upon right ventricular senses, and the left ventricular sensing channel is rendered refractory after a first ventricular sense for a specified time period. In the case where the first ventricular sense is a far-field signal due to a right ventricular depolarization, a subsequently detected left ventricular depolarization occurring during the same cardiac cycle is thus ignored and not regarded as an additional left ventricular sense. In another embodiment, a right ventricular sense triggers a cross-chamber left ventricular refractory period. This prevents the left ventricular sensing channel from interpreting a far-field signal due to a right ventricular depolarization as a left ventricular sense.